Method and apparatus for mitigating interference in a wireless communication system supportng heterogeneous networks

ABSTRACT

A method and apparatus for mitigating interference in a wireless communication system supporting heterogeneous networks are disclosed. When the wireless communication system includes a first network and a second network, the method includes generating information indicating whether each of uplink component carriers is used for transmission of control information in the first network, and transmitting the information to a UE. A component carrier used for transmission of control information in the first network is different from a component carrier used for transmission of control information in the second network.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for mitigating interferencein a wireless communication system supporting heterogeneous networks.

BACKGROUND ART

With reference to FIG. 1, a frame structure for a wireless communicationsystem will first be described. FIG. 1 illustrates a frame structure fora Long Term Evolution (LTE) system. Referring to FIG. 1, a frameincludes 10 subframes, each subframe having 2 slots. Time taken totransmit one subframe is called a Transmission Time Interval (TTI). Forexample, one subframe may be 1 ms long and one slot may be 0.5 ms long.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols. An OFDM symbol may also be called a SingleCarrier-Frequency Division Multiple Access (SC-FDMA) symbol or a symbolperiod.

One slot includes 7 or 6 OFDM symbols depending on the length of aCyclic Prefix (CP). In the LTE system, a normal CP and an extended CPare defined. One slot includes 7 OFDM symbols in the case of a normalCP, whereas one slot includes 6 OFDM symbols in the case of an extendedCP.

FIG. 2 illustrates the resource structure of one downlink slot. Herein,a slot includes 7 OFDM symbols. A Resource Element (RE) is a resourcearea occupying one OFDM symbol by one subcarrier, and a Resource Block(RB) is a resource area occupying a plurality of OFDM symbols by aplurality of subcarriers. For instance, an RB may include 7 OFDM symbolsin time by 12 subcarriers in frequency. The number of RBs per slot maybe determined according to a downlink bandwidth.

FIG. 3 illustrates a downlink subframe structure. Referring to FIG. 3,up to three first OFDM symbols in the first slot of a subframecorrespond to a control region to which a control channel is allocated.The other OFDM symbols correspond to a data region to which a PhysicalDownlink Shared Channel (PSCH) is allocated.

In the 3^(rd) Generation Partnership Project (3GPP) LTE system, downlinkcontrol channels include a Physical Control Format Indicator Channel(PCFICH), a Physical Downlink Control Channel (PDCCH), and a PhysicalHybrid automatic repeat request Indicator Channel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels in the subframe. The PHICH delivers anACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal as a responseto uplink transmission. Control information transmitted on the PDCCH iscalled Downlink Control Information (DCI). The DCI includes uplinkscheduling information, downlink scheduling information, or an uplinktransmit power control command for a User Equipment (UE).

Now a description will be given of carrier aggregation in anLTE-Advanced (LTE-A) system with reference to FIG. 4.

FIG. 4( a) illustrates a single carrier structure and FIG. 4( b)illustrates a multi-carrier structure.

As there has been an increasing demand for high data rates, studies havebeen conducted on carrier aggregation. Referring to FIG. 4( b), a UE maysimultaneously receive downlink signals on multiple carriers. However,even when a Base Station (BS) manages N downlink Component Carriers(CCs), the BS may allocate M downlink CCs to a UE so that the UEmonitors signals on the M downlink CCs. Herein, M is equal to or lessthan N. The BS may also allocate L CCs as primary CCs to the UE so thatthe UE monitors signals on the L CCs with priority. L is equal to orless than M.

If UEs of heterogeneous networks communicate with a BS in the samefrequency band in a heterogeneous network environment, interference mayoccur. For example, in the case where a femtocell BS is installed withinthe coverage of a macro BS, if UE A near to a femtocell managed by thefemtocell BS communicates with the femtocell BS and UE B near to UE Acommunicates with the macro BS in the same frequency band as UE A, asignal that UE B transmits to the macro BS interferes with UE A.Especially, considering that the Modulation and Coding Scheme (MCS)level of a Physical Uplink Control Channel (PUCCH) is not changed much,it is difficult to decrease the power of a control channel transmittedby UE A. Accordingly, the PUCCH transmitted by UE A may interfere withthe femtocell significantly.

DISCLOSURE OF INVENTION Technical Problem

As described above, interference may occur in a heterogeneous networkenvironment.

An object of the present invention devised to solve the problem lies ona method for mitigating interference in a heterogeneous networkenvironment.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

Solution to Problem

The object of the present invention can be achieved by providing amethod for mitigating interference at a BS of a first network in awireless communication system supporting carrier aggregation, includingthe first network and a second network, the method including generatinginformation indicating whether each of uplink component carriers is usedfor transmission of control information in the first network, andtransmitting the information to a UE. A component carrier used fortransmission of control information in the first network is differentfrom a component carrier used for transmission of control information inthe second network.

The information may indicate a set of component carriers not used fortransmission of control information in the first network.

The information may indicate a set of component carriers used fortransmission of control information in the first network.

The BS may receive from the UE Uplink Control Information (UCI)piggybacked to Physical Uplink Shared Channels (PUSCH) of the componentcarriers used for transmission of control information in the firstnetwork.

The BS may receive from the UE Physical Random Access Channels (PRACH)on the component carriers used for transmission of control informationin the first network.

In another aspect of the present invention, provided herein is a methodfor mitigating interference at a UE of a first network in a wirelesscommunication system supporting carrier aggregation, including the firstnetwork and a second network, the method including receiving from a BSinformation indicating whether each of uplink component carriers is usedfor transmission of control information in the first network, andtransmitting to the BS uplink control information on at least onecomponent carrier used for transmission of control information accordingto the received information. A component carrier used for transmissionof control information in the first network is different from acomponent carrier used for transmission of control information in thesecond network.

In another aspect of the present invention, provided herein is a BS of afirst network in a wireless communication system supporting carrieraggregation, including the first network and a second network, whichincludes a processor for generating information indicating whether eachof uplink component carriers is used for transmission of controlinformation in the first network, and a transmission module fortransmitting the information to a UE. A component carrier used fortransmission of control information in the first network is differentfrom a component carrier used for transmission of control information inthe second network.

In another aspect of the present invention, provided herein is a UE of afirst network in a wireless communication system supporting carrieraggregation, including the first network and a second network, whichincludes a reception module for receiving from a BS informationindicating whether each of uplink component carriers is used fortransmission of control information in the first network, and atransmission module for transmitting to the BS uplink controlinformation on at least one component carrier used for transmission ofcontrol information according to the received information. A componentcarrier used for transmission of control information in the firstnetwork is different from a component carrier used for transmission ofcontrol information in the second network.

In a further aspect of the present invention, provided herein is amethod for mitigating interference at a BS of a first network in awireless communication system supporting carrier aggregation, includingthe first network and a second network, the method including determiningfor a first UE a set of component carriers not used for transmission ofcontrol information among uplink component carriers, and notifying thefirst UE of the determined set of component carriers. The determinedcomponent carriers are used for transmission of control information inthe second network interfered by the first UE.

ADVANTAGEOUS EFFECTS OF INVENTION

According to embodiments of the present invention, interference can bemitigated in a heterogeneous network environment.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 illustrates a frame structure for a Long Term Evolution (LTE)system.

FIG. 2 illustrates the resource structure of one downlink slot.

FIG. 3 illustrates a downlink subframe structure.

FIG. 4( a) illustrates a single carrier structure and FIG. 4( b)illustrates a multi-carrier structure.

FIG. 5 illustrates transmission of a Physical Uplink Control Channel(PUCCH) and a Physical Uplink Shared Channel (PUSCH) on an uplinkComponent Carrier (CC).

FIG. 6 illustrates deployment of a macrocell and a femtocell.

FIG. 7 illustrates a method for mitigating interference according to anembodiment of the present invention.

FIG. 8 illustrates a method for mitigating interference according toanother embodiment of the present invention.

FIG. 9 is a block diagram of an Advanced Mobile Station (AMS) and anAdvanced Base Station (ABS) for implementing the above embodiments ofthe present invention, according to an embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention. The following detaileddescription includes specific details in order to provide a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout such specific details. For example, the following detaileddescription is given under the assumption that a 3^(rd) GenerationPartnership Project Long Term Evolution-Advanced (3GPP LTE-A) is beingused. However, the description is applicable to any other mobilecommunication system except for specific features inherent to the 3GPPLTE-A system.

In some instances, known structures and devices are omitted, or areshown in block diagram form focusing on important features of thestructures and devices, so as not to obscure the concept of the presentinvention. The same reference numbers will be used throughout thisspecification to refer to the same or like parts.

In the following description, a User Equipment (UE) is assumed to referto a mobile or fixed user end device such as a Mobile Station (MS), anAdvanced MS (AMS), etc. and the term ‘Base Station (BS)’ is assumed torefer to any node of a network end, such as a Node B, an enhanced Node B(eNB or eNode B), an Advanced BS (ABS), etc., communicating with a UE.

Signal transmission in a heterogeneous network environment will bedescribed below with reference to FIGS. 5 and 6.

FIG. 5 illustrates transmission of a Physical Uplink Control Channel(PUCCH) and a Physical Uplink Shared Channel (PUSCH) on an uplink CC.Referring to FIG. 5, the PUCCH and the PUSCH are transmitted indifferent frequency bands of the same uplink CC.

FIG. 6 illustrates deployment of a macrocell and a femtocell. Referringto FIG. 6, the femtocell is located within the coverage of the macrocelland two uplink CCs are used commonly in the femtocell and the macrocell.The femtocell covers a smaller area than the macrocell and services UEsnear to a femto BS. Because the coverage of the macrocell is much largerthan the femtocell, the transmit power of UE_B communicating with amacro BS is larger than the transmit power of UE_C communicating withthe femto BS. Therefore, when UE_B is near to UE_C, the transmit powerof UE_B may significantly interfere with signal transmission from UE_C.

The macro BS may control reduction of the transmit power of UE_B so thatthe transmit power of UE_B does not interfere much with the femtocell.If the transmit power of UE_B is decreased, the MCS level of a PUSCH maybe adjusted to satisfy the reception performance of the PUSCH at the BS.However, it is difficult to decrease the transmit power of a PUCCHbecause the MCS level of the PUCCH does not change much. Thus PUCCHstransmitted by UEs communicating with the macro BS may cause a greatinterference with the femtocell.

With reference to FIG. 7, a description will be given of a method formitigating interference in a wireless communication system supportingheterogeneous networks according to an embodiment of the presentinvention.

FIG. 7 illustrates a method for mitigating interference according to anembodiment of the present invention. While a macro network and a femtonetwork are taken as an example in this embodiment, to which the presentinvention is not limited, it is to be clearly understood that thepresent invention is applicable to any case in which heterogeneousnetworks are deployed.

According to the embodiment of the present invention, a BS generatesinformation indicating whether each uplink CC is used for transmittingcontrol information and transmits the information to UEs. ComponentCarriers (CCs) that are not used to transmit control information arereferred to as a PUCCH-less CC set and CCs used to transmit controlinformation are referred to as a PUCCH transmission CC set.

Referring to FIG. 7, a first CC (CC1) is a PUCCH-less CC for thefemtocell and a second CC (CC2) is a PUCCH-less CC for the macrocell. Onthe other hand, CC2 is a PUCCH transmission CC for the femtocell and CC1is a PUCCH transmission CC for the macrocell.

That is, different CCs serve as PUCCH transmission CCs in the femtocelland the macrocell.

Since the PUCCH transmission CC of the femtocell is the PUCCH-less CC ofthe macrocell, the macrocell may mitigate interference by decreasing thetransmit power of the PUCCH transmission CC of the femtocell. That is,the macro BS may command UE_B to decrease the transmit power of CC2 inorder to reduce interference in FIG. 7.

A PUCCH transmission CC set or a PUCCH-less CC set may be indicated byinformation indicating whether each uplink CC includes controlinformation. That is, the macro BS may notify UEs of a PUCCHtransmission CC set or a PUCCH-less CC set. To notify the UEs of thePUCCH transmission CC set or the PUCCH-less CC set, the macro BS may usea Broadcast Channel (BCH), common Radio Resource Control (RRC)signaling, or dedicated RRC signaling.

In addition, the macro BS may allocate uplink CCs and downlink CCs toUEs by dedicated RRC signaling.

A UE does not transmit an ACK/NACK for downlink data on a PUCCH-less CC.A PUSCH of a PUCCH-less CC is not piggybacked with Uplink ControlInformation (UCI). This is because the reception performance of UCI isnot ensured due to low transmit power of a PUCCH-less CC. To prevent aPhysical Random Access Channel (PRACH) transmitted at a high power levelfrom causing interference, the PRACH may be prohibited from beingtransmitted on a PUCCH-less CC. In other words, the UCI may bepiggybacked to a PUSCH of a PUCCH transmission CC and the PRACH may betransmitted on a PUCCH transmission CC.

With reference to FIG. 8, a method for mitigating interference accordingto another embodiment of the present invention will be described below.

FIG. 8 illustrates a method for mitigating interference according toanother embodiment of the present invention.

In accordance with this embodiment, a BS generates informationindicating whether each uplink CC carries control information andtransmits the information to UEs.

While a PUCCH-less CC set and a PUCCH transmission set are cell-specificin the embodiment illustrated in FIG. 7, a PUCCH-less CC set and a PUCCHtransmission set may be UE-specific in the embodiment illustrated inFIG. 8.

Referring to FIG. 8, a first CC (CC1) serves as a PUCCH-less CC for UE_Cand a second CC (CC2) serves as a PUCCH-less CC for UE_B. On the otherhand, CC2 serves as a PUCCH transmission CC for UE_C and CC1 serves as aPUCCH transmission CC for UE_B. Both CC1 and CC2 serve as PUCCHtransmission CCs for UE_A. Because UE_A is far from the femtocell,transmission of control information on any CC from UE_A does notinterfere with the femtocell. Therefore, UE_A is allowed to use all CCsas PUCCH transmission CCs. That is, the BS may determine a PUCCH-less CCand a PUCCH transmission CC for individual UEs.

This embodiment advantageously increases resource use flexibilitybecause a PUCCH-less CC and a PUCCH transmission CC are determined on aUE basis.

Even though a PUCCH-less CC and a PUCCH transmission CC are determinedon a UE basis, it may be regulated that UCI is not piggybacked to aPUSCH of a PUCCH-less CC and a PRACH is not transmitted on a PUCCH-lessCC. In other worlds, the UCI may be piggybacked to a PUSCH of a PUCCHtransmission CC and the PRACH may be transmitted on a PUCCH transmissionCC.

FIG. 9 is a block diagram of an AMS and an ABS for implementing theabove embodiments of the present invention, according to an embodimentof the present invention.

Referring to FIG. 9, the ABS and the AMS include antennas 900 and 910for transmitting and receiving information, data, signals and/ormessages, Transmission (Tx) modules 940 and 950 for transmittingmessages by controlling the antennas 900 and 910, Reception (Rx) modules960 and 970 for receiving messages by controlling the antennas 900 and910, memories 980 and 990 for storing information related tocommunication with the AMS and the ABS, and processors 920 and 930 forcontrolling the Tx modules 940 and 950, the Rx modules 960 and 970, andthe memories 980 and 990. Herein, the ABS may be a femto BS or a macroBS.

The antennas 900 and 910 transmit signals generated from the Tx modules940 and 950 over the air or transmit signals received over the air tothe Rx modules 960 and 970. When Multiple Input Multiple Output (MIMO)is supported, each of the AMS and the ABS may have two or more antennas.

In general, the processors 920 and 930 provide overall control to theABS and the AMS. Particularly, the processors 920 and 930 may perform acontrol function, a Medium Access Control (MAC) frame conversion controlfunction according to service characteristics and a propagationenvironment, a handover function, and an authentication and encryptionfunction in order to perform the above-described embodiments of thepresent invention. In addition, each of the processors 920 and 930 mayfurther include an encryption module for controlling encryption ofvarious messages and a timer module for controlling transmission andreception of various messages.

The processor 920 of the ABS generates information indicating whethereach uplink CC is used to transmit control information. This informationmay be cell-specific or AMS-specific.

A CC used for transmission of control information in another co-locatednetwork is determined not to be used for transmission of controlinformation.

The Tx modules 940 and 950 may encode and modulate a signal and/or datascheduled by the processors 920 and 930 in a predetermined MCS andtransmit the modulated signal and/or data to the antennas 900 and 910.

The Tx module 940 of the ABS transmits the information indicatingwhether each uplink CC is used for transmission of control informationto the AMS.

The Tx module 950 of the AMS transmits uplink control information to theABS on a CC used for transmission of control information based on thereceived information.

The Rx modules 960 and 970 may recover original data by decoding andde-modulating radio signals received through the antennas 900 and 910and may transmit the original data to the processors 920 and 930.

The Rx module 970 of the AMS receives the information indicating whethereach uplink CC is used for transmission of control information from theABS.

The Rx module 960 of the ABS receives the control information on the CCused for transmission of control information from the AMS. The Rx module960 of the ABS may receive UCI piggybacked to a PUSCH of a CC used fortransmission of control information and may receive a PRACH on a CC usedfor transmission of control information.

The memories 980 and 990 may store programs for processing andcontrolling in the processors 920 and 930 and temporarily storeinput/output data (an uplink grant allocated by an ABS, systeminformation, a Station Identifier (STID), a Flow ID (FID), an actiontime, resource allocation information, and frame offset information inthe memory 990 of the AMS).

Also, each of the memories 980 and 990 may include at least one of aflash memory-type storage medium, a hard disc-type storage medium, amultimedia card micro-type storage medium, a card-type memory (e.g. aSecure Digital (SD) or extreme Digital (XS) memory), a Random AccessMemory (RAM), a Static RAM (SRAM), a Read-Only Memory (ROM), anElectrically Erasable Programmable Read-Only Memory (EEPROM), aProgrammable Read-Only Memory (PROM), a magnetic memory, a magneticdisc, and optical disk.

MODE FOR THE INVENTION

Various embodiments have been described in the best mode for carryingout the invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a wireless communication system.More particularly, the present invention is applicable to a method andapparatus for mitigating interference in a wireless communication systemsupporting heterogeneous networks.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents. For instance, an embodiment ofthe present invention may be constructed by combining parts of theabove-described embodiments.

The above embodiments are therefore to be construed in all aspects asillustrative and not restrictive. The scope of the invention should bedetermined by the appended claims and their legal equivalents, not bythe above description and all changes coming within the meaning andequivalency range of the appended claims are intended to be embracedtherein.

1. A method for mitigating interference at a Base Station (BS) of afirst network in a wireless communication system supporting carrieraggregation, including the first network and a second network, themethod comprising: generating information indicating whether each ofuplink component carriers is used for transmission of controlinformation in the first network; and transmitting the information to aUser Equipment (UE), wherein a component carrier used for transmissionof control information in the first network is different from acomponent carrier used for transmission of control information in thesecond network.
 2. The method according to claim 1, wherein theinformation indicates a set of component carriers not used fortransmission of control information in the first network.
 3. The methodaccording to claim 1, wherein the information indicates a set ofcomponent carriers used for transmission of control information in thefirst network.
 4. The method according to claim 3, further comprisingreceiving from the UE Uplink Control Information (UCI) piggybacked toPhysical Uplink Shared Channels (PUSCH) of the component carriers usedfor transmission of control information in the first network.
 5. Themethod according to claim 3, further comprising receiving from the UEPhysical Random Access Channels (PRACH) on the component carriers usedfor transmission of control information in the first network.
 6. Amethod for mitigating interference at a User Equipment (UE) of a firstnetwork in a wireless communication system supporting carrieraggregation, including the first network and a second network, themethod comprising: receiving from a Base Station (BS) informationindicating whether each of uplink component carriers is used fortransmission of control information in the first network; andtransmitting to the BS uplink control information on at least onecomponent carrier used for transmission of control information accordingto the received information, wherein a component carrier used fortransmission of control information in the first network is differentfrom a component carrier used for transmission of control information inthe second network.
 7. The method according to claim 6, wherein theinformation indicates a set of component carriers not used fortransmission of control information in the first network.
 8. The methodaccording to claim 6, wherein the information indicates a set ofcomponent carriers used for transmission of control information in thefirst network.
 9. A Base Station (BS) of a first network in a wirelesscommunication system supporting carrier aggregation, including the firstnetwork and a second network, the BS comprising: a processor forgenerating information indicating whether each of uplink componentcarriers is used for transmission of control information in the firstnetwork; and a transmission module for transmitting the information to aUser Equipment (UE), wherein a component carrier used for transmissionof control information in the first network is different from acomponent carrier used for transmission of control information in thesecond network.
 10. The BS according to claim 9, wherein the informationindicates a set of component carriers not used for transmission ofcontrol information in the first network.
 11. The BS according to claim9, wherein the information indicates a set of component carriers usedfor transmission of control information in the first network.
 12. The BSaccording to claim 11, further comprising a reception module forreceiving from the UE Uplink Control Information (UCI) piggybacked toPhysical Uplink Shared Channel (PUSCH)s of the component carriers usedfor transmission of control information in the first network.
 13. The BSaccording to claim 11, further comprising a reception module forreceiving from the UE Physical Random Access Channel (PRACH)s on thecomponent carriers used for transmission of control information in thefirst network.
 14. A User Equipment (UE) of a first network in awireless communication system supporting carrier aggregation, includingthe first network and a second network, the UE comprising: a receptionmodule for receiving from a Base Station (BS) information indicatingwhether each of uplink component carriers is used for transmission ofcontrol information in the first network; and a transmission module fortransmitting to the BS uplink control information on at least onecomponent carrier used for transmission of control information accordingto the received information, wherein a component carrier used fortransmission of control information in the first network is differentfrom a component carrier used for transmission of control information inthe second network.
 15. The UE according to claim 14, wherein theinformation indicates a set of component carriers not used fortransmission of control information in the first network.
 16. The UEaccording to claim 14, wherein the information indicates a set ofcomponent carriers used for transmission of control information in thefirst network.
 17. A method for mitigating interference at a BaseStation (BS) of a first network in a wireless communication systemsupporting carrier aggregation, including the first network and a secondnetwork, the method comprising: determining for a first User Equipment(UE) a set of component carriers not used for transmission of controlinformation among uplink component carriers; and notifying the first UEof the determined set of component carriers, wherein the determinedcomponent carriers are used for transmission of control information inthe second network interfered by the first UE.
 18. The method accordingto claim 17, wherein a second UE located in the first network and notinterfering with the second network uses the determined componentcarriers for transmission of control information.